Electrodeposition of zinc



latented July 8, 1952 I'M-UNITED 2,602,775 7 ELEo'rRonEPosi'rIoNengineEldon is'nerwood, FlinajlulilQMiritoba, Canada, assign'or to Hudson; BayMining and 'Smelting 00., Limited,

. Canada, a corporation oilfiariaida.

nipeg, Manitoba,

No Drawing Application .septofiiber 22, 1950, Serial No. 186,323. InCanada August 10,119.50

6 Claims. 1

This invention relates to the electrodeposition of zinc from zincsulphate solutions using lead base alloy anodes. By lead base alloyanodes is meant anodes formed of an alloy consisting chiefly of lead.

As is well known, it is desirable in the electrodeposition of zinc fromzinc sulphate solutions to use anodes consisting of lead or consistingchiefly of that metal, and indeed it is generally considered that suchanodes are the only ones suitable. Such anodes are, however, subject tothe disadvantage that, during the operation of the electrolytic cell,some of the lead from the anode is transferred to the cathode zincdeposit, thereby contaminating it, and decreasing the value of the zincproduced. For certain purposes, such as pressure die casting, it isessential that zinc be almost free from certain impurities, one of themost objectionable of which is lead.

Many attempts have been made to decrease this lead transfer from'anodeto cathode and various lead base alloys have been proposed for use asanode material. Some of these lead base alloys have been partiallysuccessful, the most popular lead base alloy anode in use at present inthe electrolytic zinc industry consisting of lead and a small amount ofsilver varying up to about 2.0% by weight. Other investigators havefound that the addition of tin or tin and cobalt to this basiclead-silver alloy gives good results.

It has now been found that the use of a lead base alloy anode containingsmall amounts of copper as well as small amounts of silver, has a verypronounced and surprising effect in reducing the transfer of lead fromanode to cathode. Actual tests have shown a reduction in the amount oflead found in the cathode zinc of as much as about two-thirds when alead base alloy anode containing small amounts of copper as well assmall amounts of silver is used in place of the usual lead base alloyanode, consisting of lead and silver. It has also been found that thereis an even greater improvement over lead-silver anodes when there isused a lead base alloy anode, consisting of lead and small amounts ofsilver, copper, cobalt and manganese.

Thus, according to the invention, zinc is deposited from a zinc sulphatesolution with an alloy anode consisting essentially of lead alloyed withsmall amounts of silver and copper, the percentage of silver beingadvantageously within the range of about 0.3% to about 1.45%, and ofcopper being about 0.1% to about 0.4%. It has been found that the bestresults are obtained with such an alloy anode containing about 1%silver, about 0.25% copper and the balance lead.

According to the invention, the electrodeposition of zinc from a zincsulphate solution may also be carried out to advantage with a lead basealloy anode consisting essentially of lead alloyed with small amounts ofsilver, copper, cobalt and manganese, the percentages falling within theranges of from about 0.4% to about 1.45% silver, from about 0.15% toabout 0.45% copper, from about 0.01% to about 0.02% cobalt and fromabout 0.01% to about 0.15% manganese. It has been found that the bestproportions for an alloy anode of this composition are about 1.0%silver, about 0.5% copper, about 0.02% cobalt, and about 0.1% manganese.

The effect of carrying out the electrodeposition with thelead-silver-copper and lead-silver-copper-cobalt-manganese alloy anodesin reducing the transfer of lead from anode to cathode, as compared witha lead-silver anode, is illustrated by the following table showing theresults of laboratory tests. The percentages given are by weight and, ineach case, the remainder of the anode is lead.

Assays of Anodes Percentage A r of li N ssay o opera on Test 3.5%;Cathode with lead I\ o. of Test Ag Cu 00 Mn Zn Pb in cathode Per Per PerPer Per Cent zinc Cent Cent Cent Cent 0.0010% or less.

l. 0 Nil Nil Nil 0. 0038 2 78 0. 28 0. l2 Nil Nil 0. 0022 12 78 0. 96 0.25 Nil Nil 0.0015 46 78 1. l2 0. 21 Nil Nil 0. 0013 48 78 1. 45 0. 40Nil Nil 0. 0014 40 78 0. 36 0. l5 01 01 0. 0020 19 7 78 0.75 0.20 01 060. 0014 31 8 78 1.03 0.35 01 0. 11 0.0012 63 9 78 1. 45 0.45 01 0. 140.0011 57 10 84 0.98 0.75 02 06 0. 0012 79 11 84 0. 47 0.32 .01 .02 0.0010 63 What I claim as my invention is 1. A process for theelectrodeposition of zinc from a zinc sulphate solution, which comprisescausing deposition of zinc from the solution with an alloy anodeconsisting essentially of lead alloyed with small amounts of silver andcopper.

2. A process for the electrodeposition of zinc from a zinc sulphatesolution, which comprises causing deposition of zinc from the solutionwith an alloy anode consisting essentially of lead alloyed with smallamounts of silver, copper, cobalt and manganese.

3. A process for the electrodeposition of zinc from a zinc sulphatesolution as defined in claim 3 1, in which the amounts or silver andcopper respectively present in the alloy anode are within the ranges offrom about 0.3% to about 1.4% silver and from about 0.1% to about 0.4%copper.

4. A process for the electrodeposition of zinc from a zinc sulphatesolution as defined in claim 3, in which the amount of silver present inthe alloy anode is about 1.0% and of copper is about 0.25%.

5. A process for the electrodeposition of zinc from a zinc sulphatesolution as defined in claim 2, in which the amounts of silver, copper,cobalt and manganese respectively present in the alloy anode are withinthe ranges of from about 0.4% to about 1.45% silver, from about 0.15% toabout 0.45% copper, from about 0.01% to about 0.15% manganese, and fromabout 0.01% to about 0.02% cobalt.

5 0.5%, of cobalt is about 0.02% and of manganese is about 0.1%.

ELDON IRWIN ISHERWOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 15 Number Name Date 1,681,272 Yoshikawa Aug. 21,1928 1,699,761 Silberstein Jan. 22, 1929 2,419,722 Lowe et al Apr. 29,1947

1. A PROCESS FOR THE ELECTRODEPOSITION OF ZINC FROM A ZINC SULPHATESOLUTION, WHICH COMPRISES CAUSING DEPOSITION OF ZINC FROM THE SOLUTIONWITH AN ALLOY ANODE CONSISTING ESSENTIALLY OF LEAD ALLOYED WITH SMALLAMOUNTS OF SILVER AND COPPER.